Optimize your render time. Episode 5 – Cycles Materials

Putting this week’s post together was a bit of a challenge because while I have worked a bit with Cycles, I still haven’t acquired the kind of experience you get after going through many projects. I started on the assumption that Cycles materials do influence a lot the rendering time but was baffled by how to optimize Cycles materials. There are no settings in the materials panel that would take a bit from the realism and speed up the render like in BI, so I thought that one way to use materials effectively in Cycles was to compare the different shaders, and learn to wisely pick the best ones for a specific scene. I made a kind of benchmark test with all the shaders and posted it on Blender Artists hoping to get opinions from you and other Cycles fans.

The test shows that two shaders that are noticeable slower to render are glass and translucency. This was not surprising but the next result was unexpected to me: the glossy shader renders faster than the diffuse one. I still avoided overuse of reflective / glossy objects in Cycles as I did in BI, so this changed my perspective on materials a lot. But glossy is still tricky, having large glossy surfaces in the scene might render faster for the same number of samples, but they also introduce a lot of noise and fireflies. There are things you can do to improve noise and enjoy the glossy materials, here are three of them:

Turn the glossy bounces down in the Light path panel (render tab). Lower settings will give less noise (and render faster). However, bounces are good for the realistic look of the material, so test for a low setting that won’t take all the life out of your gloss.

Use lower color values under 0.8 for the shaders. If materials appear too dark, try increasing the light in the scene some more instead of just lightening the color.

And the best: the clamp setting in the render tab. The default zero value does nothing, a value different from zero will put a max limit on some light values bounced around, making fireflies magically go away. If the values are too low some specular spots you like might disappear too so it’s a matter of testing on your particular scene. For a test I did clamp=1 worked great.

The subject of noise and fireflies is explained in technical detail in the Blender Wiki, complete with interesting tips like those above.